Optimal Defense Theory Research Articles

Surface sequestration of chemical feeding deterrents in the Antarctic sponge Latrunculia apicalis as an optimal defense against sea star spongivory

Latrunculia apicalis is a spherically shaped demosponge that previous investigations have shown is rarely preyed upon by sea stars which are the dominant spongivores in antarctic benthic communities. Prior studies have also demonstrated that L. apicalis produces organic compounds that elicit a tube foot retraction response in the keystone spongivorous sea star Perknaster fuscus that can be used as a reliable assay for feeding deterrence. L. apicalis is known to contain discorhabdin alkaloids which serve, among other roles, as the source of its green coloration. To assess the defensive nature of the discorhabdin alkaloids toward P. fuscus, we have determined discorhabdin G concentrations in discrete sponge layers and evaluated those concentrations in the P. fuscus bioassay. In discorhabdin G-bearing sponges, we found a gradient of discorhabdin G that falls off rapidly toward the center of the sponge. On average, 52% of total discorhabdin G in a given sponge was found within 2 mm of the sponge surface. Tube foot retraction responses to extracts from the surface tissues (0–2 mm depth) of L. apicalis were compared to those of an inner layer (8–10 mm depth) and to a sample comprised of the same inner layer spiked with discorhabdin G at a concentration equivalent to that of the surface tissues. Tube foot retraction response times to extracts of the surface layers and the spiked inner layers were not statistically different, but were significantly greater than responses to the unaltered inner layer and controls. These results support the predictions of the optimal defense theory as L. apicalis sequesters its defensive chemistry (discorhabdin G) in its most vulnerable surface tissues, where the likelihood of predation from sea stars is highest. As antarctic sponges are generally preyed upon by extraoral feeding sea stars rather than deeper biting predators such as fish, surface sequestration may be uniquely adaptive in sessile macroinvertebrates occurring in antarctic marine benthic environments.

Tissue-specific palatability and chemical defenses against macropredators and pathogens in the common articulate brachiopod Liothyrella uva from the Antarctic Peninsula

The punctate terebratulid brachiopod Liothyrella uva is the most common brachiopod species in Antarctica. Whole brachiopods, either live or freeze dried and ground into a powder and suspended in alginate, were unpalatable to the sympatric macropredators Odontaster validus (an abundant, omnivorous sea star) and Notothenia coriiceps (an abundant, omnivorous, epibenthic fish). The unpalatability of these ground tissues coupled with that of lipophilic extracts of whole L. uva presented in alginate pellets to O. validus, suggests an involvement of chemical defenses. Several isolated brachiopod tissues were also unpalatable to O. validus after being freeze dried, ground and suspended in alginate, but only the pedicle was unpalatable in such preparations to both O. validus and N. coriiceps. This observation is consistent with the Optimal Defense Theory since the pedicle is the only tissue not protected inside the brachiopod shell. There was, however, no correlation between the energetic content and unpalatability of any of the individual tissues. Organic extracts of tissues involved in feeding (lophophore and intestine–stomach) had relatively strong antimicrobial activity when assayed against several strains of Antarctic bacteria. However, the lophophore was palatable to both macropredators, suggesting nonoverlapping chemical defenses are involved in protection against predators and pathogens.

To grow and defend: lack of tradeoffs for brown algal phlorotannins

The concept of cost is an integral element of ecological theories, including optimal defense theory, resource availability theory, and growth‐differentiation balance theory. Indeed most frameworks that attempt to explain within‐plant patterns of secondary metabolites, as well as account for the evolution of induced defenses, presume that defenses are ‘costly’. One way in which investigators have sought to quantify the cost of secondary metabolites is to examine growth/defense tradeoffs, which are predicted to occur wherever resources cannot be simultaneously allocated to both growth and defense. However, emerging evidence suggests that these critical assumptions may not be valid for brown algal phlorotannins, compounds that occur throughout the division Phaeophyta and have served as analogs to vascular plant tannins in numerous tests of terrestrial‐derived ecological theories in the marine environment. Here we present a model of phlorotannins as metabolites with both primary and secondary roles and argue that apparent trade‐offs between algal growth and phlorotannin content are not a reliable indicator for establishing a cost of defense. We suggest the ecological theories which presume that defenses are costly because resources allocated to defense cannot also be allocated to other ‘primary’ functions are unlikely to accurately predict the striking variations in algal phlorotannin concentrations that are observed in nature.

Is induction response negatively correlated with constitutive resistance in black mustard?

Black mustard, Brassica nigra, is highly variable in both constitutive resistance and induction response following damage by herbivores. A focal population from Ithaca, New York, was used to test the following two predictions of optimal defense theory: (1) that allocation to resistance will reduce plant performance in the absence of herbivores; and (2) that induction response will be negatively correlated with constitutive resistance. The experiment consisted of a half-sib mating design with 47 paternal families and four dams per sire, fully crossed with a damage treatment consisting of 25% leaf removal by the cabbage white butterfly, Pieris rapae, when plants had four leaves. Leaf trichome density, sinigrin concentration, and glucobrassicin concentration were 38%, 19%, and 16% higher, respectively, for the seventh leaf of damaged plants. Paternal families did not vary significantly in their induction response. Narrow-sense heritabilities were h(S)(2) = 0.51, 0.76, and 0.50 for constitutive leaf trichome density, sinigrin concentration, and glucobrassicin concentration, respectively. Positive genetic correlations were found between glucobrassicin concentration and days to first flower, suggesting a genetic cost of resistance. Induction responses were negatively correlated with constitutive allocation for leaf trichome density and sinigrin concentration. The results were therefore consistent with optimal defense theory, offering modest evidence for both predictions.

Tissue-specific induction of herbivore resistance: seaweed response to amphipod grazing.

Tissues within individual plants can vary greatly in the strength of their constitutive (i.e., permanent) and induced resistance to herbivores. Optimal defense theory predicts that defenses should be allocated among tissues in proportion to the value of the tissues to the plant and the tissue-specific risk of attack by grazers. We examined the relationship between tissue value and defense in the highly-differentiated brown seaweed Sargassum filipendula. Tissues within S. filipendula varied widely in palatability to the herbivorous amphipod Ampithoe longimana, with younger tissues preferred over older tissues and blades preferred over stipes. Old stipes (at the base of the plant), which linked the other tissues to the seafloor and were thus the most valuable tissue to the plant, were defended constitutively and resisted amphipod grazing by virtue of their toughness rather than via deterrent chemistry. Induction of resistance as a result of amphipod grazing occurred only in the top stipes, which contain the meristematic tissue responsible for future growth. Induction in the top stipes was not due to toughness or other structural properties, as the unpalatability persisted when top stipes were dried, ground to a fine powder, and reconstituted into an agar matrix. This suggests that the induced resistance to grazing resulted from an increase in chemical defenses. The demonstration of constitutive or induced defenses in only the more valuable tissues of the seaweed is consistent with predictions of optimal defense theory. Our finding of induction due to mesograzer (amphipod) feeding is also consistent with the notion that it is these small, more sedentary, herbivores that are most likely to induce defenses in seaweeds.

OPTIMAL DEFENSE THEORY: ELASTICITY ANALYSIS AS A TOOL TO PREDICT INTRAPLANT VARIATION IN DEFENSES

Optimal defense theory (ODT) predicts that plants should have the highest defense levels in parts that have the highest value in terms of fitness. Assumptions about differences in fitness value among plant parts have previously been based on general reasoning, e.g., that reproductive tissue is more valuable than vegetative tissue since fitness ultimately depends on reproduction. Here we present a first example of how demographic elasticity (proportional sensitivity) analysis can be used as a tool to generate more objective and specific estimates of the fitness value of different plant parts, based on the entire life cycle. These estimates were further used to generate testable predictions about intraplant variation in defenses of the brown seaweed Ascophyllum nodosum (knotted wrack). The predictions were clearly supported by the results from both analyses of chemical defense levels (phlorotannins) and bioassays (feeding preference experiments), which showed that reproductive tissues had the lowest defense level of the three examined tissue types, in contrast to previous assumptions. We suggest that a stronger focus on variation in life history among species and populations, with demographic perturbation analysis as one important tool, could lead to a better understanding of intraplant variation in defense levels, in seaweeds as well as vascular plants and other modular organisms.

Optimal Defense Theory: Elasticity Analysis as a Tool to Predict Intraplant Variation in Defenses

Optimal Defense Theory: Elasticity Analysis as a Tool to Predict Intraplant Variation in Defenses

Changes in the glucosinolate-myrosinase defense system in Brassica juncea cotyledons during seedling development.

Optimal defense theory (ODT) predicts that plant defenses will be allocated to plant organs and tissues in proportion to their relative fitness values and susceptibilities to attack. This study was designed to test ODT predictions on the myrosinase-glucosinolate defense system in Brassica juncea by examining the relationships between the fitness value of B. juncea cotyledons and the levels and effectiveness of cotyledon defenses. Specifically, we estimated fitness value of cotyledons during plant development by measuring plant growth and seed production after cotyledon damage or removal at successive seedling ages. Cotyledon removal within five days of emergence had a significant impact on growth and seed production, but cotyledon removal at later stages did not. Consistent with ODT, glucosinolate and myrosinase levels in cotyledons also declined with seedling age, as did relative defenses against a generalist herbivore, Spodoptera eridania, as estimated by bioassay. Declines in glucosinolates were as predicted by a passive, allometric dilution model based on cotyledon expansion. Declines in myrosinase activity were significantly more gradual than predicted by allometric dilution, suggesting active retention of myrosinase activity as young cotyledons expand.

IS INDUCTION RESPONSE NEGATIVELY CORRELATED WITH CONSTITUTIVE RESISTANCE IN BLACK MUSTARD?

Black mustard, Brassica nigra, is highly variable in both constitutive resistance and induction response following damage by herbivores. A focal population from Ithaca, New York, was used to test the following two predictions of optimal defense theory: (1) that allocation to resistance will reduce plant performance in the absence of herbivores; and (2) that induction response will be negatively correlated with constitutive resistance. The experiment consisted of a half-sib mating design with 47 paternal families and four dams per sire, fully crossed with a damage treatment consisting of 25% leaf removal by the cabbage white butterfly, Pieris rapae, when plants had four leaves. Leaf trichome density, sinigrin concentration, and glucobrassicin concentration were 38%, 19%, and 16% higher, respectively, for the seventh leaf of damaged plants. Paternal families did not vary significantly in their induction response. Narrow-sense heritabilities were h2s = 0.51, 0.76, and 0.50 for constitutive leaf trichome density, sinigrin concentration, and glucobrassicin concentration, respectively. Positive genetic correlations were found between glucobrassicin concentration and days to first flower, suggesting a genetic cost of resistance. Induction responses were negatively correlated with constitutive allocation for leaf trichome density and sinigrin concentration. The results were therefore consistent with optimal defense theory, offering modest evidence for both predictions.

Phenols in reproductive and somatic structures of lichens: a case of optimal defence?

Optimal defence theory (ODT) attempts to explain variation in plant secondary compounds between different species, different growth conditions and different parts of individual plants. The theory is widely applied to vascular plants and more recently also to seaweeds. Surprisingly, ODT has gained little attention as potential explanation on the distribution of lichen secondary metabolites. In the present study, we analysed intrathalline variation in total phenol content and phenol spectra between reproductive and somatic structures of three foliose lichens, Xanthoria parietina, Vulpicida pinastri and Hypogymnia physodes. The results showed that the concentration of phenolic compounds is higher in sorediate than in non‐sorediate lobe ends of V. pinastri and H. physodes as well as in apothecia of X. parietina compared to other parts of the thallus. These results were in accordance with ODT predicting higher allocation of phenols in structures that are most important for the fitness of an individual genet or ramet. This pattern was parallel in all species regardless whether the compounds originate from either acetate‐mevalonate or shikimic acid pathways. Moreover, both sexual (X. parietina apothecia) and asexual (soralia of V. pinastri and H. physodes) reproductive structures were higher in phenols compared to somatic tissue.

OPTIMAL DEFENSE THEORY PREDICTS THE ONTOGENY OF AN INDUCED NICOTINE DEFENSE

Optimal Defense (OD) theory predicts that the within-plant allocation of secondary metabolites that function as defenses will be positively correlated with the fitness value of particular plant parts. Here, we experimentally examine this prediction by ex- ploiting our understanding of the mechanisms of wound-induced nicotine production in Nicotiana sylvestris (Solanaceae) to manipulate the patterns of nicotine allocation and to determine their fitness consequences. In two perturbation experiments conducted over three stages of ontogeny (rosette, elongation, and flowering), we wounded or removed leaves of different ages (young, mature, or old) and determined the effects on nicotine allocation (whole-plant and within-plant) and fitness (lifetime viable seed production). OD theory predicts that, as leaves age and their fitness value decreases, the allocation of defense to particular leaves and the fitness consequences of their removal should be positively cor- related. We found that (1) leaf removal results in a significant decrease in seed mass at the elongation stage, but not at the rosette or flowering stages; (2) the relative value of leaves decreases from young and mature to old leaves; (3) leaf damage significantly increases the whole-plant nicotine contents of rosette-stage plants, but not of elongation- or flowering- stage plants, and after damage, younger leaves are more heavily defended than older leaves at the elongation and flowering stages; and (4) regardless of ontogenetic stage, plants distribute nicotine among leaves in accordance with their relative fitness value, thus sup- porting OD theory predictions. Leaf value increases after N fertilization at the flowering stage, but is not changed if adjacent leaves are removed at earlier growth stages. Moreover, plants are capable of sending their root-synthesized nicotine to specific leaves after damage; at the elongation stage, the new and young leaves receive greater proportional allocations of nicotine than other leaves. The cessation of significant whole-plant nicotine inductions at later stages in ontogeny is not due to the root's decreased ability to respond to the plant's wound signal, jasmonic acid (JA) with increased nicotine biosynthesis, but rather to the decline in a leaf's sensitivity to wounding and in its ability to export JA from the leaves to roots. Ontogeny has profound effects on the use of this induced defense. Plants mount systemic nicotine inductions at the rosette stage that rely on large increases in de novo nicotine synthesis, switch to the selective targeting of nicotine to the new and young leaves at the elongation stage without large increases in de novo nicotine synthesis, and allocate to reproductive structures, but not leaves, at the flowering stage. These changes are consistent with the predictions of OD theory.

Optimal Defense Theory Predicts the Ontogeny of an Induced Nicotine Defense

Optimal Defense (OD) theory predicts that the within-plant allocation of secondary metabolites that function as defenses will be positively correlated with the fitness value of particular plant parts. Here, we experimentally examine this prediction by exploiting our understanding of the mechanisms of wound-induced nicotine production in Nicotiana sylvestris (Solanaceae) to manipulate the patterns of nicotine allocation and to determine their fitness consequences. In two perturbation experiments conducted over three stages of ontogeny (rosette, elongation, and flowering), we wounded or removed leaves of different ages (young, mature, or old) and determined the effects on nicotine allocation (whole-plant and within-plant) and fitness (lifetime viable seed production). OD theory predicts that, as leaves age and their fitness value decreases, the allocation of defense to particular leaves and the fitness consequences of their removal should be positively correlated. We found that (1) leaf removal results in a significant decrease in seed mass at the elongation stage, but not at the rosette or flowering stages; (2) the relative value of leaves decreases from young and mature to old leaves; (3) leaf damage significantly increases the whole-plant nicotine contents of rosette-stage plants, but not of elongation- or flowering-stage plants, and after damage, younger leaves are more heavily defended than older leaves at the elongation and flowering stages; and (4) regardless of ontogenetic stage, plants distribute nicotine among leaves in accordance with their relative fitness value, thus supporting OD theory predictions. Leaf value increases after N fertilization at the flowering stage, but is not changed if adjacent leaves are removed at earlier growth stages. Moreover, plants are capable of sending their root-synthesized nicotine to specific leaves after damage; at the elongation stage, the new and young leaves receive greater proportional allocations of nicotine than other leaves. The cessation of significant whole-plant nicotine inductions at later stages in ontogeny is not due to the root's decreased ability to respond to the plant's wound signal, jasmonic acid (JA) with increased nicotine biosynthesis, but rather to the decline in a leaf's sensitivity to wounding and in its ability to export JA from the leaves to roots. Ontogeny has profound effects on the use of this induced defense. Plants mount systemic nicotine inductions at the rosette stage that rely on large increases in de novo nicotine synthesis, switch to the selective targeting of nicotine to the new and young leaves at the elongation stage without large increases in de novo nicotine synthesis, and allocate to reproductive structures, but not leaves, at the flowering stage. These changes are consistent with the predictions of OD theory.

Specialist weevil, Rhyssomatus lineaticollis, does not spatially avoid cardenolide defenses of common milkweed by ovipositing into pith tissue

Rhyssomatus lineaticollis is a milkweed specialist whose larvae feed upon pith parenchyma in ramet stems of the common milkweed, Asclepias syriaca. Compared with other specialist insect herbivores on milkweeds, this curculionid beetle is unusual in that it is cryptically colored and does not sequester cardenolides characteristic of milkweed chemical defense. Based upon optimal defense theory, we predicted that pith tissue would be low in defensive compounds and that oviposition into the pith would spatially avoid cardenolides. We rejected this hypothesis because we found that pith tissue has a relatively high cardenolide concentration compared to cortex, epidermis, and leaf tissues. Moreover, we found total plant cardenolide concentration was lower in plants that contained the beetle eggs. Cardenolide concentrations were different among tissues in intact stems without the pith herbivore compared to stems where it was present. Furthermore, the overall polarity of the cardenolides present varied among plant tissues and between plants with and without R. lineaticollis eggs. Although we found lower concentrations of cardenolide in piths where the eggs were present, the cardenolides present in the pith contained more nonpolar forms, indicating that the plant may be responding to herbivory by increasing toxic efficacy of cardenolide defenses while lowering the total concentration. We suggest that preoviposition behavior by female beetles, which includes feeding on new leaves of the plant, is a mechanism by which females manipulate plant chemistry and assess quantitative and qualitative changes in cardenolide chemistry in response to herbivory prior to oviposition.

Distribution of secondary metabolites in the sponge Oceanapia sp. and its ecological implications

The Micronesian sponge Oceanapia sp. has an unusual growth form that consists of an irregular turnip-shaped base, which is buried in the substrate. One to several fistules, which protrude through the sand, are attached to the base of the sponge. On top of each fistule is a small fragile capitum. We examined whether this conspicuous red-colored sponge was chemically defended and if intraspecimen variation existed in the distribution of secondary metabolites between different parts of the sponge. Furthermore we assessed the deterrent properties of the secondary metabolites to generalist and more specialized fish predators. We also wanted to see if the optimal defense theory holds in the case of a marine invertebrate. According to the theory, organisms evolve and allocate defenses in a way that maximizes individual fitness, assuming that defenses are costly to the fitness of the organisms. We were able to evaluate this hypothesis, since the different sponge parts in Oceanapia sp. were at different risk to damage by predators and had a different value in terms of fitness loss to the sponge (the capitum probably plays a role in asexual propagation). Concentrations of crude organic extract increased from the base to the capitum of the sponge. The major secondary metabolites kuanoniamine C and D also showed a sharp increase from the basal root to the capitum. There was no difference in structural material or ash content between the base and the fistule of the sponge, but fiber and protein content were significantly higher in the fistule. The methanol fraction was highly deterrent in field feeding assays towards generalist reef fish at base concentration. It also deterred feeding by the spongivorous angelfish Pomacanthus imperator in laboratory feeding experiments at the same concentration. The field feeding assays with pure compounds showed that kuanoniamine C and D deterred feeding by natural assemblages of reef fishes at fistule concentrations, confirming their role as defensive agents. The intraspecimen variation of secondary metabolites in Oceanapia sp. supports the optimal defense theory by showing the highest concentrations in those parts of the sponge that are most visible to predators and are likely to be most important for inclusive fitness.

PHLOROTANNIN ALLOCATION AMONG TISSUES OF NORTHEASTERN PACIFIC KELPS AND ROCKWEEDS

Optimal defense theory (ODT) predicts antiherbivore defensive compounds will be allocated so that the most valuable or most susceptible tissues will be best defended. The growth–differentiation balance hypothesis (GDBH) predicts that defense allocation will be a result of trade‐offs between growth and defense. Thus, these two theories predict opposite allocation patterns with respect to “valuable,” actively growing meristematic and reproductive tissues. ODT predicts that meristems and reproductive tissues should have higher defense levels than nonmeristematic vegetative tissues; the GDBH predicts the defense levels of meristems and reproductive tissues will be lower than vegetative tissues. We examined allocation patterns of phlorotannins in 21 species of kelps (Order Laminariales) and rockweeds (Order Fucales) from nine sites on the west coast of the United States to determine if allocation patterns better matched the predictions of ODT or the GDBH and to look for differences in allocation patterns among sites. Within‐species differences in phlorotannin levels occurred in 10 of the 21 species examined. Meristems of both kelps and rockweeds had higher phlorotannin levels than nonmeristematic vegetative tissues, consistent with ODT. Phlorotannin levels in reproductive tissues of kelps were higher than vegetative tissues, but levels in reproductive tissues of rockweeds were lower than vegetative tissues, indicating that allocation strategies may follow taxonomic lines. Allocation patterns differed among sites in four of the 16 species collected from more than one site. Differences in allocation patterns among sites were usually changes in the ratios of phlorotannins in well‐defended compared to poorly defended tissues, rather than changes in which tissues were well defended or poorly defended. We concluded that environmental variability can have large effects on the concentration of phlorotannins in algae but has limited effects on allocation patterns among tissues.

Optimal defence, kin conflict and the distribution of furanocoumarins among offspring of wild parsnip

The factors influencing the allocation of chemical defences to plant offspring have largely been unexplored, conceptually and experimentally. Because evolutionary interactions between maternal plants and their progeny can affect resource allocation patterns among sibling offspring, we suggest that kin conflict as well as herbivore–plant interaction theories need to be considered to predict chemical defence allocation patterns. Optimal defence theory predicts that maternal plants should defend more heavily those offspring in which resources have been disproportionately invested. In contrast, kin conflict theory predicts that natural selection will favour genotypes that can compete successfully for maternal defences irrespective of their quality, even at the expense of the fitness of siblings and the maternal plant. Evidence for these defence patterns were evaluated by examining the allocation of furanocoumarins to seeds of the wild parsnip (Pastinaca sativa, Apiaceae). Furanocoumarins are toxins that are localized within the oil tubes of the maternal tissues of seeds. We evaluated the role of offspring investment (endosperm mass) and seed genotype on furanocoumarin allocation by mating an array of pollen donors with pollen recipients. Furanocoumarins were found to be positively correlated with endosperm mass on one side of the seed, a result consistent with optimal defence theory; however, on the other side of the seed, furanocoumarin content was influenced by seed genotype and was unrelated to endosperm mass. These effects varied with maternal plant. Further experiments demonstrated that nearly 80% of furanocoumarin production occurs after pollination, when fertilization products are active. Although the amount of furanocoumarin influenced by the seed genotype is small relative to the total quantity in the seed, these furanocoumarins are the first line of defence against important predators, such as the parsnip webworm, Depressaria pastinacella (Lepidoptera: Oecophoridae). We found that parsnip webworm larvae were able to discriminate among genotypes within an inflorescence. In line with previous studies, these results suggest that a genotype's ability to influence furanocoumarin defence may affect its probability of survival. We conclude that the distribution of defences among plant offspring in wild parsnip is probably influenced by competition among seed genotypes that conflicts with maternal optimal defence.

Effect of defoliation on the patterns of allocation of a hydroxamic acid in rye ( Secale cereale)

Hydroamic acids are a class of secondary metabolites typical of grasses which play a role in resistance to herbivores. The effects of defoliation (simulated herbivory) on the allocation patterns of a hydroxamic acid (DIBOA) in rye seedlings were evaluated. Defoliated plants were compared with undefoliated plants 5, 7, 9 and 11 days after defoliation and germination, respectively. Shoot DIBOA of defoliated and undefoliated seedlings decreased with increasing age, but DIBOA concentration in defoliated seedlings was generally higher than in undefoliated ones. On the other hand, DIBOA concentration of the primary leaf was not affected by defoliation. The contribution of the primary leaf to the DIBOA content of the whole shoot as well as to the biomass of the whole shoot decreased with time for both defoliation treatments. As age increased the primary leaf of undefoliated seedlings decreased in relative DIBOA content at a greater rate than in relative biomass. The primary leaf of defoliated seedlings showed a similar rate of decrease for both variables. This pattern as well as that for DIBOA concentration in defoliated vs. undefoliated seedlings was interpreted as consistent with predictions of the Optimal Defense theory. In addition, the increased level of DIBOA in the shoot and, to a lesser extent, the unchanged DIBOA level in primary leaf of defoliated seedlings supported an extension of the ‘reversion to juvenile phase’ phenomenon described for woody plant-mammal interactions.

Within-plant relationships among wounding, jasmonic acid, and nicotine implications for defence in Nicotiana sylvestris.

In Nicotiana sylvestris Spegazzini and Comes (Solanaceae), we examined the relationships among wounding, endogenous leaf jasmonic acid (JA) pools, and whole-plain (WP) nicotine accumulation over a range of wounding intensities and spatial distributions, in order to explore optimal defence (OD) theory predictions. We quantitatively wounded one or four leaves and then quantified: (1) JA in damaged and undamaged leaves 90 min after wounding; (2) WP nicotine concentration after 5 d (the times when JA and nicotine attain the largest wound-induced concentrations). We find: (1) statistically significant, positive relationships on a leaf-by-leaf basis among the number of leaf punctures, endogenous leaf JA, and WP nicotine accumulation; (2) that young, undamaged leaves have a higher concentration of JA than do older, undamaged leaves, and produce a greater amount of JA per puncture than older leaves, but that all leaves have the same JA content (ng JA per leaf); and (3) that a damaged leaf produces less JA when other leaves in the canopy are wounded than when it is the onh wounded leaf in the canopy, but that when it is the only wounded leaf, the phylotactically adjacent, undamaged leaves do not increase their JA concentrations. The observation that younger leaves produce more JA per puncture than do older leaves is consistent with OD theory predictions. The observation that a small amount of damage localized to a single leaf is as effective as a larger amount of damage dispersed across the canopy in increasing leaf JA and WP nicotine accumulation shows the plant's ability to differentiate between dispersed and localized damage. Because the quantity of JA in a wounded leaf 90 min after wounding is a reliable indicator of the WP nicotine response to wounding, this trait provides insight into how plants integrate information about environmental insults and tailor their defence responses.

Lack of Costs of Herbivory-Induced Defenses in a Wild Wheat: Integration of Physiological and Ecological Approaches

Aphid infestation triggered a significant induction of hydroxamic acids (Hx) in wild wheat Triticum (uniaristatum seedlings in comparison to control seedlings. We hypothesized that indirect costs of Hx induction (expressed in plant fitness parameters) would be found if such induction was a consequence of enhanced local synthesis of Hx at the infested tissue and would not if the significantly less costly translocation of Hx was established to be the process underlying the induction. Results obtained following whole-plant analysis after aphid infestation suggested translocation of Hx from the stem as the process underlying the observed Hx induction in the infested leaf. Then, as expected, non-significant differences in growth, size and survival between control and infested plants were found. The present work stresses the importance of unraveling the sources of induced defenses in the understanding of the observed patterns of defense allocation in plants. The consistency of the results obtained with the predictions of the Optimal Defense theory was also discussed.

The Probability of Attack and Patterns of Constitutive and Induced Defense: A Test of Optimal Defense Theory

Optimal defense theory predicts that tissues that are unlikely to be attacked by herbivores should have low constitutive amounts of defense and high inducibility, while tissues that are likely to be attacked should have high levels of constitutive defense and low inducibility. We artificially damaged roots, leaves, and reproductive parts of wild parsnip (Pastinaca sativa L.) and found that these parts differ not only in constitutive levels of chemical defense but also in the degree to which these defenses are inducible. Reproductive parts contain the highest constitutive concentrations of a toxic furanocoumarin, xanthotoxin, but xanthotoxin production is not inducible in these parts. Roots contain the lowest constitutive levels of xanthotoxin and are highly inducible. Leaves are intermediate in both the constitutive amounts of xanthotoxin they contain and inducibility. To test the prediction of optimal defense theory, we surveyed three populations of wild parsnip for the presence of damage to roots, leave...